In the exploration, drilling, and production of hydrocarbons, it becomes necessary to drill directional and horizontal wells. As those of ordinary skill in the art appreciate, directional and horizontal wells can increase the production rates of reservoirs. Hence, the industry has seen a significant increase in the number of directional and horizontal wells drilled. Additionally, as the search for hydrocarbons continues, operators have increasingly been targeting thin beds and/or seams with high to very low permeability. The industry has also been targeting unconventional hydrocarbon reservoirs such as tight sands, shales, and coal.
Traditionally, these thin bed reservoirs, coal seams, shales and sands may range from less than five feet to twenty feet. In the drilling of these thin zones, operators attempt to steer the drill bit within these zones. As those of ordinary skill in the art will recognize, keeping the well bore within the zone is highly desirable for several reasons including, but not limited to, maintaining greater drilling rates, maximizing production rates once completed, limiting water production, preventing well bore stability problems, exposing more productive zones, etc.
Various prior art techniques have been introduced. However, all these techniques suffer from several problems. For instance, in the oil and gas industry, it has always been an accepted technique to gather surface and subsurface information and then map or plot the information to give a better understanding of what is actually happening below the earth's surface. Some of the most common mapping techniques used today include elevation contour maps, formation contour maps, sub sea contour maps and formation thickness (isopac) maps. Some or most of these can be presented together on one map or separate maps. For the most part, the information that is gathered to produce these maps are from electric logging and real time measurement while drilling and logging devices (gamma ray, resistivity, density neutron, sonic or acoustic, surface and subsurface seismic or any available electric log). This type of data is generally gathered after a well is drilled. Additionally, measurement while drilling and logging while drilling techniques allow the driller real time access to subterranean data such as gamma ray, resistivity, density neutron, and sonic or acoustic and subsurface seismic. This type of data is generally gathered during the drilling of a well.
These logging techniques have been available and used by the industry for many years. However, there is a need for a technique that will utilize historical well data and real time down hole data to steer the bit through the zone of interest. There is a need for a method that will produce, in real time during drilling, an instantaneous dip for a very thin target zone. There is also a need for a process that will utilize the instantaneous dip to produce a calculated target window (top and bottom) and extrapolate this window ahead of the projected well path so an operator can keep the drill bit within the target zone identified by the calculated dip and associated calculated target window.
In the normal course of drilling, it is necessary to perform a survey. As those of ordinary skill in the art will appreciate, in order to guide a wellbore to a desired target, the position and direction of the wellbore at any particular depth must be known. Since the early days of drilling, various tools have been developed to measure the inclination and azimuth of the wellbore.
In order to calculate the three dimensional path of the wellbore, it is necessary to take measurements along the wellbore at known depths of the inclination (angle from vertical) and azimuth (direction normally relative to true north). These measurements are called surveys.
Prior art survey tools include those run on wireline such as but not limited to steering tools as well as those associated with measurement while drilling (MWD), electro-magnetic measurement while drilling (EM-MWD) and magnetic single shot (MSS). Hence, after drilling a hole section, a wireline survey is run inside the drill pipe before pulling out with the drill bit, or by running a wireline survey inside the steel casing once it is cemented in place. During drilling, many government regulations require the running of a wireline survey or getting an MWD survey, or EM-MWD survey, such as in some cases every 200 feet for horizontal wells and every 500 feet for deviated wells.
In today's environment of drilling and steering in ultra-thin target zones, knowing the true stratigraphic position and direction of the bit within the true stratigraphic formation is critical. Operators need to know the accurate position of the bit and bit projection path. In the event of an actual deviation from a planned strata-graphic wellbore projection path, time is critical in order to correct the bit direction back to the planned true stratigraphic path to prevent the bit from drilling into nonproductive zones.